Carbonyls commercial availability

The replacement of selenoamide by selenourea in the Hantzsch s synthesis. (1st method) leads to 2-aminoselenazoles 2, 14. 15). This series of compounds has been well developed, mainlv because selenourea is much more easily accessible than the selenoamides, but also because a wide variety of a-halogenated carbonyl compounds are available for the Hantzsch s evdization reaction (Scheme 5). 2-Aminoselenazole itself was prepared from commercially available chloroacetaldehyde semihydrate... 

The gases used in the CVD reactor may be either commercially available gases in tanks, such as Ar, N2, WF, SiH, B2H, H2, and NH Hquids such as chlorides and carbonyls or soflds such as Mo carbonyl, which has a vapor pressure of 10 Pa (75 mtorr) at 20°C and decomposes at >150° C. Vapor may also come from reactive-bed sources where a flowing haUde, such as chlorine, reacts with a hot-bed material, such as chromium or tantalum, to give a gaseous species. 

Thiophenecarboxaldehyde [498-62-4] has been commercially available (35) via carbonylation of 2,5-dimethoxy-2,5-dihydrofuran, followed by treatment with hydrogen sulfide, which introduces the sulfur atom with loss of methanol, inducing aromaticity and producing 3-thiophenecarboxaldehyde directly. 

Low Pressure Syntheses. The majority of metal carbonyls are synthesized under high pressures of CO. Early preparations of carbonyls were made under superpressures of 1 GPa (ca 10,000 atm). Numerous reports have appeared in the Hterature concerning low pressure syntheses of metal carbonyls, but the reactions have been restricted primarily to the carbonyls of the transition metals of Groups 8—10 (VIII). A procedure for preparing Mn2(CO)2Q, however, from commercially available methylcyclopentadienyknanganese tricarbonyl [12108-13-3] and atmospheric pressures of CO has been reported (117). The carbonyls of mthenium (118,119), rhodium (120,121), and iridium (122,123) have been synthesized in good yields employing low pressure techniques. In all three cases, very low or even atmospheric pressures of CO effect carbonylation. Examples of successful low pressure syntheses are... 

Table 5 Hsts the metal carbonyls that are commercially available and the corresponding U.S. manufacturers or suppHers. Companies produciag these compounds on a captive basis are not iacluded.

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

The most common method of epoxidation is the reaction of olefins with per-acids. For over twenty years, perbenzoic acid and monoperphthalic acid have been the most frequently used reagents. Recently, m-chloroperbenzoic acid has proved to be an equally efficient reagent which is commercially available (Aldrich Chemicals). The general electrophilic addition mechanism of the peracid-olefin reaction is currently believed to involve either an intra-molecularly bonded spiro species (1) or a 1,3-dipolar adduct of a carbonyl oxide, cf. (2). The electrophilic addition reaction is sensitive to steric effects. 

The commercially available (tj5-cyclopentadienyl)iron dicarbonyl dimer 1 is the source of the carbonyl(//5-cyclopentadienyl)iron(L) moiety. Reductive or oxidative cleavage of 1 provides reactive monomeric species that may be converted into iron-acyl complexes as described in the following sections (see also Houben-Weyl, Vol. 13/9a, p208). 

Many metal carbonyls are available commercially. However, in some cases, the CVD investigator may find it more expedient (and sometimes cheaper) to produce them in-house. This is particularly true of the only two carbonyls that can be obtained by the direct reaction of the metal with CO (and consequently easy to synthesize), i.e., nickel carbonyl, Ni(CO)4, and iron carbonyl, Fe(CO)5. 

N-Acetylneuraminic acid aldolase (or sialic acid aldolase, NeuA EC 4.1.3.3) catalyzes the reversible addition of pyruvate (2) to N-acetyl-D-mannosamine (ManNAc (1)) in the degradation of the parent sialic acid (3) (Figure 10.4). The NeuA lyases found in both bacteria and animals are type I enzymes that form a Schiff base/enamine intermediate with pyruvate and promote a si-face attack to the aldehyde carbonyl group with formation of a (4S) configured stereocenter. The enzyme is commercially available and it has a broad pH optimum around 7.5 and useful stability in solution at ambient temperature [36]. 

Finally, because of the close relationship between silicon and tin, carbonyl compounds such as phenylacetaldehyde afford with the commercially available bis[bis(trimethylsilyl)amino]tin(II) 561, which is prepared by reaction of li-HMDS 492 with SnCl2, the N,N-bis(trimethylsilylated)enamine 562, in 85% yield, and SnO [131, 132] (Scheme 5.41). 

The first chiral phases introduced for gas chromatography were either amino acid esters, dipeptide, diamide or carbonyl-bis(amino acid ester) phases [721,724,756-758]. In general, these phases exhitdted poor thermal stability and are infrequently used today. Real interest and progress in chiral separations resulted from the preparation of diamide phases grafted onto a polysiloxane backbone. These phases were thermally stable and could be used to prepare efficient open tubular columns [734,756,758-762]. These phases are prepared from commercially available poly(cyano-propylmethyldimethylsiloxanes) or poly (cyanopropylmethylphenyl-... 

The parent methylenecyclopropane (MCP) (1) [1 ] is a highly volatile compound (bp 11 °C) which can be prepared in multigram quantities and is commercially available. Numerous efficient and straightforward syntheses of the different types of methylene- and alkylidenecyclopropanes have appeared in the literature and the matter has been reviewed by Binger and Buch [2]. In the last decade other selective syntheses have been developed which gave easy access to compounds containing specific substitution patterns [3], to optically active derivatives [4], or more sophisticated derivatives like dicyclopropylideneethane (2) [5], bicyclopropylidene (BCP) (3) [6] and chloromethoxy carbonyl-methylenecyclopropane (4) [7],... 

Materials. The commercially available aldehydes were distilled prior to use and stored at 0°C under argon. The cyclohexene- and cyclopentene- aldehydes, and the indane aldehyde (see Table) were gifts from Professor E. Piers of this department. The Ru(TPP)(PPh3)2 complex (1) was prepared from Ru(TPP)(CO)(EtOH) and PPh3 (1,7), while Ru(TPP)(CO)(tBu2POH), was prepared from the carbonyl (ethanol) adduct by treatment with tBu2PCl (1). The phosphines were from Strem Chemicals, and the ruthenium was obtained as RuCl Ol O from Johnson, Matthey Limited. 

Enzyme reductions of carbonyl groups have important applications in the synthesis of chiral compounds (as described in Chapter 10). Dehydrogenases are enzymes that catalyse, for example, the reduction of carbonyl groups they require co-factors as their co-substrates. Dehydrogenase-catalysed transformations on a practical scale can be performed with purified enzymes or with whole cells, which avoid the use of added expensive co-factors. Bakers yeast is the whole cell system most often used for the reduction of aldehydes and ketones. Biocatalytic activity can also be used to reduce carbon carbon double bonds. Since the enzymes for this reduction are not commercially available, the majority of these experiments were performed with bakers yeast1 41. 

One of the fundamental operations in organic synthesis remains the stereoselective reduction of carbonyl groups1241. In a process related to that reported by Hosomi et u/.[25], using hydrosilanes as the stoichiometric oxidant and amino acid anions as the catalytic source of chirality, a variety of ketones were reduced in good to excellent yield and with good stereoselectivity1261. This process reduces the amount of chiral catalyst needed and utilizes catalysts from the chiral pool that can be used directly in their commercially available form. 

The most convenient method of preparing the flexible (low Tg) system is to employ the Ullmann ether reaction of dibromobenzene and aromatic bis-diols followed by catalytic replacement of the bromine atoms by terminal acetylene groups. A host of commercially available bis-diols have been used in the synthesis with both meta and para dibromobenzene. Low Tg arylether oligomers have been prepared containing sulfone, sulfide, carbonyl, isopropyl and perfluoroisopropyl groups in the backbone (9). 

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